Re: [Bugme-new] [Bug 15342] New: max_address parameter is not taken into consideration when IPv6 addresses are created

Re: [Bugme-new] [Bug 15342] New: max_address parameter is not taken into consideration when IPv6 addresses are created

[Andrew Morton]

(switched to email.  Please respond via emailed reply-to-all, not via the
bugzilla web interface).

On Wed, 17 Feb 2010 14:12:28 GMT bugzilla-daemon@bugzilla.kernel.org wrote:

> http://bugzilla.kernel.org/show_bug.cgi?id=15342
> 
>            Summary: max_address parameter is not taken into consideration
>                     when IPv6 addresses are created
>            Product: Networking
>            Version: 2.5
>     Kernel Version: 2.6.32.5
>           Platform: All
>         OS/Version: Linux
>               Tree: Mainline
>             Status: NEW
>           Severity: low
>           Priority: P1
>          Component: IPV6
>         AssignedTo: yoshfuji@linux-ipv6.org
>         ReportedBy: nedyalkor@gmail.com
>         Regression: No
> 
> 
> >From ip-sysctl.txt file in kernel documentation I can see following description
> for max_addresses:
> max_addresses - INTEGER
>         Number of maximum addresses per interface.  0 disables limitation.
>         It is recommended not set too large value (or 0) because it would
>         be too easy way to crash kernel to allow to create too much of
>         autoconfigured addresses.
>         Default: 16
> 
> On my machine all parameters are set to default value 16:
> # sysctl -a|grep max_addresses
> net.ipv6.conf.all.max_addresses = 16
> net.ipv6.conf.default.max_addresses = 16
> net.ipv6.conf.lo.max_addresses = 16
> net.ipv6.conf.eth0.max_addresses = 16
> 
> To my understanding I should not be able to create more than 16 IP addresses,
> but in fact I am able do it:
> 
> # for i in `seq 1 16`; do ip addr add fec0::$i/64 dev eth0; done
> # ip addr add fec0::17/64 dev eth0
> # ip -6 addr
> 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436
>     inet6 ::1/128 scope host
>        valid_lft forever preferred_lft forever
> 2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qlen 1000
>     inet6 fec0::17/64 scope site
>        valid_lft forever preferred_lft forever
>     inet6 fec0::16/64 scope site
>        valid_lft forever preferred_lft forever
>     inet6 fec0::15/64 scope site
>        valid_lft forever preferred_lft forever
>     inet6 fec0::14/64 scope site
>        valid_lft forever preferred_lft forever
>     inet6 fec0::13/64 scope site
>        valid_lft forever preferred_lft forever
>     inet6 fec0::12/64 scope site
>        valid_lft forever preferred_lft forever
>     inet6 fec0::11/64 scope site
>        valid_lft forever preferred_lft forever
>     inet6 fec0::10/64 scope site
>        valid_lft forever preferred_lft forever
>     inet6 fec0::9/64 scope site
>        valid_lft forever preferred_lft forever
>     inet6 fec0::8/64 scope site
>        valid_lft forever preferred_lft forever
>     inet6 fec0::7/64 scope site
>        valid_lft forever preferred_lft forever
>     inet6 fec0::6/64 scope site
>        valid_lft forever preferred_lft forever
>     inet6 fec0::5/64 scope site
>        valid_lft forever preferred_lft forever
>     inet6 fec0::4/64 scope site
>        valid_lft forever preferred_lft forever
>     inet6 fec0::3/64 scope site
>        valid_lft forever preferred_lft forever
>     inet6 fec0::2/64 scope site
>        valid_lft forever preferred_lft forever
>     inet6 fec0::1/64 scope site
>        valid_lft forever preferred_lft forever
>     inet6 fe80::223:aeff:fe77:44ba/64 scope link
>        valid_lft forever preferred_lft forever
> 
>
> If this parameter applies only for auto-configured IP addressed, please state
> it more clearly in docs or rename the parameter to show that it refers to
> auto-configuration.
> 

[PATCH] IPv6: better document max_addresses parameter

[Brian Haley]

Andrew Morton wrote:
>> >From ip-sysctl.txt file in kernel documentation I can see following description
>> for max_addresses:
>> max_addresses - INTEGER
>>         Number of maximum addresses per interface.  0 disables limitation.
>>         It is recommended not set too large value (or 0) because it would
>>         be too easy way to crash kernel to allow to create too much of
>>         autoconfigured addresses.
           ^^^^^^^^^^^^^^

>> If this parameter applies only for auto-configured IP addressed, please state
>> it more clearly in docs or rename the parameter to show that it refers to
>> auto-configuration.

It did mention autoconfigured in the text, but the below makes it more obvious.


More clearly document IPv6 max_addresses parameter.

Signed-off-by: Brian Haley <brian.haley@hp.com>
---

diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index 2571a62..8b72c88 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -1126,10 +1126,10 @@ regen_max_retry - INTEGER
 	Default: 5
 
 max_addresses - INTEGER
-	Number of maximum addresses per interface.  0 disables limitation.
-	It is recommended not set too large value (or 0) because it would
-	be too easy way to crash kernel to allow to create too much of
-	autoconfigured addresses.
+	Maximum number of autoconfigured addresses per interface.  Setting
+	to zero disables the limitation.  It is not recommended to set this
+	value too large (or to zero) because it would be an easy way to
+	crash the kernel by allowing too many addresses to be created.
 	Default: 16
 
 disable_ipv6 - BOOLEAN

Re: [PATCH] IPv6: better document max_addresses parameter

[David Miller]

From: Brian Haley <brian.haley@hp.com>
Date: Mon, 22 Feb 2010 17:27:21 -0500

> Andrew Morton wrote:
>>> >From ip-sysctl.txt file in kernel documentation I can see following description
>>> for max_addresses:
>>> max_addresses - INTEGER
>>>         Number of maximum addresses per interface.  0 disables limitation.
>>>         It is recommended not set too large value (or 0) because it would
>>>         be too easy way to crash kernel to allow to create too much of
>>>         autoconfigured addresses.
>            ^^^^^^^^^^^^^^
> 
>>> If this parameter applies only for auto-configured IP addressed, please state
>>> it more clearly in docs or rename the parameter to show that it refers to
>>> auto-configuration.
> 
> It did mention autoconfigured in the text, but the below makes it more obvious.
> 
> 
> More clearly document IPv6 max_addresses parameter.
> 
> Signed-off-by: Brian Haley <brian.haley@hp.com>

Applied.